The interference of noise signal on an ECG signal is significant as it may affect the quality of the signal and may result in wrong clinical interpretation. One of the sources of the noise in the ECG signal is the power fluctuations and the interference from the power transmission line. Line frequency variation is common in many developing countries where ECG products are used for diagnostic purposes. Generally, the powerline frequency is expected to be 50 Hz or 60 Hz and this value is country specific. In some places the frequency varies from the set value.
Some of the solutions suggest eliminating the noise in ECG signals, but at least a part of the ECG signal is also removed, while removing the noise. Thus clinically relevant information is lost from the ECG signal. Existing line frequency filters do eliminate the line frequency well as long as it does not vary. In an example, when the variation exceeds more than ±0.5 Hz, the efficacy of the filter is markedly reduced.
Some of the techniques for eliminating noise includes band limiting the signal to below the powerline frequency by using low pass filters, but this will result in loss of information since attenuation is done for all frequencies above 50/60 Hz.
A notch filter at 50 Hz/60 Hz is used for eliminating the noise. This will result in removal of the powerline interference but will also remove the 50 Hz/60 Hz component present in the ECG signal. Though this may be better option, using notch filters can cause ringing in the ECG waveform, which can result in wrong interpretation and analysis of the signal.
Some examples of adaptive filters studied, would filter the powerline frequency without affecting the ECG signal, but were not effective in the face of variations in frequency.
Thus it will be beneficial to have an improved method for eliminating power line interferences in an ECG signal.